Studies of the effects of environmental agents on human health are a vital part of the mission of the institute. As such studies are almost always observational rather than experimental, interpretation of the data is complex. Good statistical collaboration in all phases, including conception, design, analysis, and interpretation, is essential to the success of this work. During the current year, we were active collaborators on many projects. Included were studies of the impact of various aspects of agricultural work on neurologic and respiratory outcomes in adults, studies of the relationship of prenatal exposures to organochlorines and fetal and later childhood outcomes, and studies of the determinants of lead exposure in children. Also included were studies aimed at better understanding of the biology of certain reproductive conditions and studies of treatment outcomes.